Build, test and ship Manifest V3 extensions

A practical cross-browser resource for building, testing, and publishing modern browser extensions. Every page leads with the constraint that bites first — service worker eviction, permission review, the API the other engine does not have, or the auto-update that landed while the user had twenty tabs open.

4 tracks · 28 topic guides · 85 in-depth pages · Chrome, Firefox and Safari differences on every page

Start with service workers Cross-browser reference

Four tracks through MV3

Pick the track that matches what you are building right now — each one ends where the next begins.

Core APIs & Data MV3 Architecture UI/UX Patterns Testing & Debugging

Browse every topic

28 guides, each with runnable code, an execution-context note under every snippet, and the Chrome, Firefox and Safari divergences spelled out.

Testing, Debugging & Performance Optimization

Unit test, end-to-end automate, debug every MV3 execution context, and profile service worker performance — a practical engineering discipline for Chrome, Firefox, and Safari extensions.

Core APIs & Cross-Browser Data Management

Master MV3 storage, messaging, declarativeNetRequest, tabs, and scripting APIs — with cross-browser compatibility patterns for Chrome, Firefox, and Safari extensions.

MV3 Architecture & Extension Lifecycle

Master Manifest V3 service workers, content scripts, popup & options UI, and store compliance — with cross-browser patterns for Chrome, Firefox, and Safari.

UI/UX Patterns & Interactive Components

Build production-ready extension UIs in MV3: popup design, options pages, keyboard shortcuts, context menus, and side panels — with accessibility, theming, and CSP patterns.

Recently added

The newest guides, covering the parts of MV3 that most often arrive late in a project — signing users in, shipping an update onto a running browser, and the accessibility work that a 360-pixel popup makes harder than it looks.

Identity & OAuth Authentication

Sign users in from a Manifest V3 extension: launchWebAuthFlow with PKCE, redirect URLs per browser, token storage that survives worker eviction, and refresh without a secret.

Extension Updates & Data Migration

Ship an update without breaking installed users: onInstalled reasons, versioned storage migrations, orphaned content scripts, and controlling when the new version takes over.

Internationalization & Accessibility

Localise and make accessible every MV3 extension surface: the i18n API, _locales bundles, CSP-safe DOM translation, keyboard navigation, RTL layouts and live announcements.

Fixing Extension Context Invalidated After an Update

Why open tabs throw Extension context invalidated after an auto-update, how to tell orphaning from worker eviction, and how to retire or re-inject the old content script.

Handling Safari Web Extension Conversion Gaps

Run safari-web-extension-converter and fix what it reports: missing APIs, the native container app, stricter permission prompts, and behaviour probes for stubbed methods.

Measuring Content Script Impact on Page Load

Quantify what your content script costs the pages it runs on: run_at trade-offs, long-task attribution, layout thrash from injected DOM, and a repeatable A/B measurement.

Start here

Coming from MV2

Your background page is now an evictable service worker, and that single change explains most of the bugs you are about to meet.

Migration guide

Building the interface

Popups, options pages, side panels and context menus — including which surface is right for state the user needs to keep visible.

UI patterns

Getting it published

Permission justifications reviewers accept, the audit that catches rejections before upload, and a release pipeline that reaches all three stores.

Submission & compliance

Shipping version two

An auto-update lands on a running browser: storage migrations that survive eviction, and the open tabs still running last week's content script.

Updates & migration